Insertion of binary messages in video pictures

ABSTRACT

A method and a circuit for marking with a binary code a video sequence compressed by motion calculation, from one picture to another, of macroblocks dividing each picture, the digital pictures being distributed in at least two categories according to whether they are coded integrally or by the motion vectors of the macroblocks with respect to the previous picture or to the previous and next pictures, which includes, at least for the pictures coded by motion vectors, only marking the macroblocks for which the motion vectors are greater than a predetermined threshold.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the insertion of codes or binarymessages of identification or authentication in digital moving picturesand, more specifically, in moving pictures compressed by a motioncalculation, area by area, from one picture to the other, for example,according to the Standard MPEG2, MPEG4, or H263.

2. Discussion of the Related Art

A first example of application relates to the insertion of an identifieror the person entitled to the rights relative to the video sequence toenable detection of a possible piracy by distribution of illicit copies.A second example of application is the protection against set-upsdeforming or falsifying the pictures of video sequences, to ensure theintegrity of a film. A third example is the insertion of rights relativeto the use of the video sequences (number of copies or of possibleuses).

The technique of binary code insertion in digital pictures is generallyknown as the “watermarking” and has had a recent expansion with therapid development of digital picture transmission, especially over theInternet. Considering the increasing risk of illicit copies, the personsentitled to royalties, in particular, have searched for means to protectmoving digital multimedia contents.

The three above examples concern so-called security applications.Non-security applications may also be found, for example, the insertingof characteristics linked to the shooting or other picture information.

Generally, the inserting of a code concerns each picture in the animatedsequence, all pictures then comprising an insertion (for example, anidentification code of the author is reproduced in all pictures). It ispossible for the content of the respective codes to be linked to thepicture sequence, to detect a possible parasitic picture insertion.

Whatever the application, a so-called marking algorithm is used toencrypt and position, in the pictures, the codes to be inserted therein.A reverse algorithm is used to restore, according to the application,the identification codes or the shooting characteristics, etc.

Many moving picture marking algorithms are known, for example, ofstandard ISO/IEC 13818-2 “Generic Coding of Moving Pictures andAssociated Audio”. The present invention does not relate to the actualmarking algorithm and applies whatever the type of algorithm used.

The modification or coding often takes the form of an addition of aspecific noise forming the hidden message. In the case of movingpictures to which the present invention applies, this noise additionresults, especially if a marking robustness requiring stronger markingis desired, in a flickering of the pictures which is unacceptable inpractice.

It could be devised not to mark all the pictures, to reduce theperception of the flickering by a human eye. However, such a solutionwould considerably weaken the marking, in particular to guarantee thepicture sequence integrity.

SUMMARY OF THE INVENTION

The present invention aims at providing a novel solution for digitallymarking pictures compressed by a motion calculation area by area fromone picture to the other, and more specifically pictures coded accordingto standard MPEG2 (such as specified in the H262 recommendations in 1995by “International Standard Tutorials”), video standard MPEG4, or H263.

The present invention especially aims at providing a solution which doesnot weaken the marking, in particular the video picture sequenceintegrity.

To achieve these and other objects, the present invention provides amethod for marking with a binary code a video sequence compressed bymotion calculation, from one picture to another, of macroblocks dividingeach picture, the digital pictures being distributed in at least twocategories according to whether they are coded integrally or by themotion vectors of the macroblocks with respect to the previous pictureor to the previous and next pictures, which comprises, at least for thepictures coded by motion vectors, of only marking the macroblocks forwhich the motion vectors are greater than a predetermined threshold.

According to an embodiment of the present invention, all the macroblocksof the pictures of the first category are marked.

According to an embodiment of the present invention, for the picturescoded by motion vectors:

the motion vectors of the macroblocks of the current picture arecalculated,

the absolute value of the motion vectors is compared with apredetermined threshold; and

according to whether the motion vector of a macroblock is or not greaterthan said threshold, the pixels of the macroblock are submitted or notto a marking algorithm.

According to an embodiment of the present invention, a prediction errorof each macroblock is calculated, be it or not submitted to the markingalgorithm, prior to an MPEG coding by discrete cosine transform.

According to an embodiment of the present invention, said threshold isselected to correspond to a motion greater than 5 pixels from onepicture to the next one.

According to an embodiment of the present invention, the presentinvention is applied to a coding according to an MPEG standard.

The present invention also provides an MPEG coding circuit.

The foregoing objects, features and advantages of the present invention,will be discussed in detail in the following non-limiting description ofspecific embodiments in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate, in very simplified views of successivepictures of a video sequence, an implementation mode of the methodaccording to the present invention;

FIG. 2 shows an embodiment of an MPEG video coding device to implementthe present invention; and

FIG. 3 is a simplified flowchart of an implementation mode of the binarymessage insertion method according to the present invention.

DETAILED DESCRIPTION

For clarity, only those method steps and those system elements that arenecessary to the understanding of the present invention have been shownin the drawings and will be described hereafter. In particular, theactual marking algorithms modify the picture sectors have not beendescribed in detail. The present invention applies whatever the markingalgorithm used. Further, the coding techniques according to standardMPEG2 are perfectly well known and have not been described in detail.

A feature of the present invention is to mark the pictures only in theregions which are modified from one picture to the next one. In otherwords, the present invention provides not marking the still areas of thepictures. Indeed, the most significant visual degradation is created inthe still or slightly moving areas of moving sequences by the noise dueto the addition of a marking.

Another feature of the present invention is to take advantage of thecoding technique, for example, an MPEG technique, to detect the stilland moving areas of the pictures. Indeed, the MPEG-type coding exploitsmotion vectors of blocks from one picture to the next one (or thepreceding one) which enable making out the moving areas from the fixedareas. As is perfectly well known, the MPEG coding uses a division intopixel blocks of the picture to be coded. These pixel blocks are calledmacroblocks.

FIG. 1A illustrates in a simplified representation of two successivepictures S_(i) and S_(i+1) an implementation mode of the presentinvention.

In FIG. 1A, picture S_(i) is assumed to be formed of a horizontal line Tat least partially contained in a first macroblock B1 and of an anglepattern A at least partially contained in a second macroblock B2.

In the next picture (S_(i+1)), it is assumed that line T has not movedwith respect to the preceding picture and that it is thus stillcontained in macroblock B1. However, angle A has changed place in thepicture and is now contained in a macroblock B3.

In a simplified manner, the MPEG coding comprises of calculating, forthe macroblocks of the next picture which are different with respect tothe preceding picture, motion vectors V which then just have to betransmitted from a transmitter to a receiver for the latter to be ableto restore picture Si+1 based on picture Si, at least for what concernsthe moving block.

According to the present invention, block B1 of picture Si+1 will not bemarked (coded by insertion of a binary message) to avoid any flickeringin this fixed area of the picture. However, the coding will be appliedto block B2 for which the noise is not visible by the eye due to theblock motion between the two successive pictures.

FIG. 2 shows, in the form of blocks, an embodiment of an MPEG codingcircuit adapted for the implementation of the present invention.

Conventionally, pictures S are first processed (block 1, FRAME ORDERING)to be distributed in three categories I, P, and B following a predefinedso-called “group of pictures” order. A first category (I) is called“Intra” and corresponds to the pictures for which all of the informationof the macroblocks forming them must be transmitted (pixel by pixel).The two other categories P and B are called “Previous” and“Bidirectional” and correspond to pictures having their macroblockscoded with reference to other pictures (previous for category P andprevious and following for category B) in the video flow.

According to the present invention, the pictures are marked differentlyaccording to the category to which they belong.

Since I pictures are coded with no reference to the other pictures(which corresponds to a so-called JPEG coding), they are the lesscompressed by the transformation. According to a preferred embodiment ofthe present invention, all their pixels are marked, even those of stillareas. Indeed, I pictures are generally very spaced apart in the videoflow (there generally are only two pictures in one second of a videoflow). Accordingly, the fact of also marking still areas poses noflickering problem (there is no succession of marked still areas in thedisplay).

As concerns the P and B pictures which refer to the previous andpossibly next images, only the picture macroblocks for which the motionvector standard is greater than a predetermined threshold are marked.

As illustrated in FIG. 2, the I pictures are marked by a processconventional per se (block 9, WATERMARK), then undergo a discrete cosinetransform (block 2, DCT) followed by a quantization (block 3, Q) beforebeing multiplexed (block 4, MUX) and written according to the propersyntax to form a flow or a file respecting the standard, for example,MPEG.

Conventionally, Intra pictures (and the Previous and Bidirectionalpictures) may be used as a base for the coding (calculation of themotion vectors) of the other pictures. For this purpose, an output ofblock 3 is sent onto an inverse transform (block 5, I-DCT), then onto aninverse quantization (block 6, I-Q) to store (block 7, BUFFER) the codedpicture upstream of a block 8 estimating the motion (MOTION ESTIMATOR)of the macroblocks of the other picture categories.

According to the embodiment shown in FIG. 2, it is provided to only markthe moving macroblocks of Previous pictures P and of Bidirectionalpictures B. The motion vectors are calculated as in a conventional MPEG2coder, the output of block 1 being connected to the input of block 8 forthe P and B pictures. After these calculations, the consideredmacroblock is marked or not according to the value of the motion vectorstandard (block 9′, WATERMARK), and this, before calculation ofestimation error EE. Then, as in a conventional coder, the estimationerror is calculated and the MPEG coding process carries on with no othermodification.

According to the present invention, when a block has been marked by abinary message, it is not necessary to recalculate the motion vector(MOTION ESTIMATOR 8) since the addition of the binary code has notmodified the scene motion. This is a significant advantage of thepresent invention since the motion vector calculation is one of the mostcomplex steps of an MPEG coding. It is thus important not to have torepeat it. However, the prediction or estimation error EE, eachmacroblock of which is the difference between that of the currentpicture and the optimal macroblock calculated by means of the motionestimation in the reference picture, is recalculated. This error is thentransferred to discrete cosine transform block 2 as in a conventionalMPEG coding. The recalculation of the estimation error has not beenshown in FIG. 2. This recalculation is performed between the output ofblock 9′ and the input of block 2 (on link 10 from block 9′ to block 2).

As an alternative, blocks 9 and 9′ may be confounded in a single circuitshared by the respective paths of the I pictures and of the P and Bpictures with appropriate sorting means.

In the case of a macroblock of a B picture which refers both to theprevious picture and to the next picture, account is preferentiallytaken of the largest motion vector (in module) among that with respectto the previous picture and that with respect to the next picture.

FIG. 3 illustrates in the form of a flowchart an implementation mode ofthe method according to the present invention for B- or P-type pictures.The P- and B-type pictures are first stored (block 20, STORE P, B).Then, the respective motion vectors MV of the macroblocks MB of thesepictures are conventionally calculated (block 21, MOTION VECTOR). Theabsolute value of the motion vector of each macroblock is then compared(block 22, ABS(MV(MB))>TH?) with a predetermined threshold TH to selectthose of the macroblocks which will be marked. The selected macroblocksare then submitted to the binary code insertion by means of aconventional algorithm (block 23, WM(MB)). Then, the prediction error isrecalculated (block 24, ERRPRED(MB)) as with the macroblocks notselected on test 22. The obtained error is then conventionally processedby compression (block 25, COMPRESS). Finally, the next macroblock (block26, NEXT MB) is selected and the calculation of its motion vector isresumed (block 21).

Once the picture is finished, it is proceeded to the next picture of theflow provided by block 1 (FIG. 2).

The above description of the method of the present invention is afunctional description. In particular, different processings in parallelmay be performed, provided that they are compatible with theconventional MPEG coding and decoding.

The reading of the marked information is performed at the MPEG decodingin a way similar to the coding process. The I pictures areconventionally decoded by an MPEG-compatible decoder and the marking isextracted from the entire pictures. As for the P and B pictures, theyare decoded, but the marking is only read in the macroblocks havingtheir motion vectors exceeding the predetermined threshold.

An advantage of the present invention is that it enables insertion ofbinary messages in a video picture sequence without for all this thatthey flicker and while inserting, preferentially, a marking in all thesequence pictures.

Another advantage of the present invention is that it is particularlysimple to implement by taking advantage of the motion vectors calculatedfor the MPEG-coded pictures.

Of course, the present invention is likely to have various alterations,modifications, and improvement which will readily occur to those skilledin the art. In particular, it generally applies whatever the markingalgorithm used.

Further, the implementation of the present invention by usingconventional tools (hardware and/or software) is within the abilities ofthose skilled in the art based on the functional indications givenhereabove.

Moreover, the setting of the threshold depends on the application andespecially on the visual quality desired regarding the flickering. Forexample, threshold TH corresponds to a motion comprised between 5 and 15pixels of the macroblock in the picture.

Finally, although the present invention has been described in relationwith an MPEG coding, it more generally applies to any moving picturecompression for which the pictures are distributed in at least twocategories according to whether they are coded integrally or by motionvectors of areas of the current picture with respect to at least oneprevious picture or to the previous and next pictures.

Such alterations, modifications, and improvements are intended to bepart of this disclosure, and are intended to be within the spirit andthe scope of the present invention. Accordingly, the foregoingdescription is by way of example only and is not intended to belimiting. The present invention is limited only as defined in thefollowing claims and the equivalents thereto.

1. A method for marking with a binary code a video sequence compressedby motion calculation, from one picture to another, of macroblocks thatform each picture, the method comprising: receiving digital pictures ofat least two categories, including a first category in which the digitalpictures are coded integrally and a second category in which the digitalpictures are coded by motion vectors of the macroblocks with respect tothe previous picture or to the previous and next pictures; and marking,for the pictures of the second category coded by motion vectors, onlythe macroblocks for which the motion vectors are greater than apredetermined threshold.
 2. The method of claim 1, comprising markingall the macroblocks of the pictures of the first category.
 3. The methodof claim 1, comprising, for the pictures coded by motion vectors:calculating the motion vectors of the macroblocks of the currentpicture, comparing the absolute value of the motion vectors with apredetermined threshold; and according to whether the motion vector of amacroblock is or not greater than said threshold, submitting or not thepixels of the macroblock to a marking algorithm.
 4. The method of claim3, wherein a prediction error of each macroblock is calculated, be it ornot submitted to the marking algorithm, prior to a coding by discretecosine transform.
 5. The method of claim 1, wherein said threshold isselected to correspond to a motion greater than 5 pixels from onepicture to the next one.
 6. The method of claim 1, applied to a codingaccording to an MPEG standard.
 7. An MPEG coding circuit, comprisingmeans for implementing the method of claim
 1. 8. A method of marking avideo, the method comprising: receiving video motion informationrepresenting a change in position of a first image portion of the video;determining whether the change in position of the first image portionexceeds a threshold; and marking the first image portion of the video,if the change in position of the first image portion exceeds thethreshold.
 9. The method of claim 8, wherein marking the first imageportion of the video comprises marking at least one pixel of the firstimage portion of the video.
 10. The method of claim 8, wherein, prior toreceiving the video motion information, the video has been compressedaccording to changes in positions of macroblocks of the video sequenceto determine the video motion information, and further comprising:determining, for each of the macroblocks, whether a change in theposition of each macroblock exceeds a threshold; and marking at leastone of the macroblocks for which the change in position exceeds thethreshold.
 11. The method of claim 10, wherein the video motioninformation comprises motion vectors for the macroblocks, and furthercomprising: comparing an absolute value of the motion vectors with athreshold; and if the absolute value of the motion vector of amacroblock is greater than the threshold, submitting pixels of themacroblock to a marking algorithm.
 12. The method of claim 10, furthercomprising: marking all the macroblocks for which the change in positionexceeds the threshold.
 13. The method of claim 8, wherein the thresholdis selected to correspond to a change in position of the first imageportion of at least 5 pixels from a first picture to a second picture ofthe video.
 14. The method of claim 8, wherein the video has beencompressed according to an MPEG standard to determine the video motioninformation.
 15. A device for marking a video, the device comprising: amotion estimator that receives video motion information representing achange in position of a first image portion of the video and determineswhether the change in position of the first image portion exceeds athreshold; and a first marking unit that marks the first image portionof the video, if the change in position of the first image portionexceeds the threshold.
 16. The device of claim 15, wherein the firstmarking unit marks the first image portion of the video by altering atleast one pixel of the first image portion of the video.